Hi,
Thanks for the interest in our plugins. I can answer your question.
When the checking process occurs in WooCommerce Tickets this function runs and it has an action in it you could hook to:
/**
* Marks an attendee as checked in for an event
*
* @param $attendee_id
*
* @return bool
*/
public function checkin( $attendee_id ) {
update_post_meta( $attendee_id, $this->checkin_key, 1 );
do_action( 'wootickets_checkin', $attendee_id );
return true;
}
EDD Tickets has a similar function, but in that the action is:
do_action( 'eddtickets_checkin', $attendee_id );
Let me know if you have any follow up questions.
Thanks